First of all in this experiment, the effect of addition of various amounts of Mo to Ni on the dissolution rate of Ni by hydrochloric acid under following conditions, in 10 percent and 20 percent boiling solutions, and in 10, 20 and 30 percents solutions at room temperature, was systematically studied and compared the resistivities of this binary alloys of various compositions with those of Hastelloy A and Nemic, the latter was prepared by the present writers and its quality was also mentioned in the fifth report. Those alloys containing more than 35 percent Mo have high degree of resistivity against concentrated hydrochloric acid at room temperature and in the solutions of various concentrations under boiling condition, although they can be hardly cast and forged. But the alloy containing 30 percent Mo could be cast, forged and rolled with a special precaution and has also a good resistivity under all conditions mentioned above. Then the improvement of the resistivity of the alloy Ni-Mo (30%) was undertaken, i. e. the respective effect of Cu, W, Cu-Be, Fe-Ta, Fe-Ti, Fe-V and Fe-Zr, which were added to replace some part of Ni in the alloy, on the resistivity against the acidic solutions under conditions mentioned above and then pure metals, Ta, Mo, W and Ag were studied and compared with the above alloys. From each series of the alloys, six or seven kinds of composition were prepared making the total of the alloys studied to be 42 kinds. As every solution in all conditions has no oxidizing action, the effect of Cr was not studied. According to these experiments, the resistivities of MO40 (Ni-40% Mo) cast alloy against the boiling hydrochloric acid of 10 and 20 percents was the greatest and the next was MOW3, MOW5, either of these alloys were of cast alloy and superior in quality as that of Nemic alloy.
As forgeablealloys, the qualities of MOV 0.3, MOV 0.5 and 1 were similar to that of Nemic and MOV 0.5 has appreciably better resistivity then that of Nemic in 10 percent boiling solution. In the solution of 10 percent at room temperature, those of the alloys studied in these experiments were not so good as those of Nemicle C and Necomicle alloys, mentioned in the second report, prepared by the present writers, but those of forgeable alloys MOZ1, MOZ2 were a little better than that of Nemic alloy in the solutions of 10 and 30 percents. As cast alloys, those of MOV5, MOTi5 and MOW10 were also superior to that of Nemic, especially that of MOW10, which was twice better than Nemic in 30 percent solution. The famous alloy Hastelloy A was not so good as those of Nemic and the alloys mentioned above. After all, under room temperature condition, Cu, V, Ta and W have a beneficial effect and under boiling condition, Cu, Zr, V and Ti gave good effect on the resistivity of the allloy Ni-Mo (30%) against hydrochloric acid.
Pure metals, Mo, W, and Ta were hardly attacked by 10 percent boiling solution and by 10, 20 and 30 percents solutons at room temperature but attacked by 20 percent solution under boiling condition. On the other hand, Ag was attacked by as much as that of Nemic by the boiling solutions of 10 and 20 percents, and the resistivity of Ag against the solutions at room temperature was the better, the stronger the concentration of the solution used.

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